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The mass reduction of passenger vehicles has been a great focus of academic research and federal policy initiatives of the United States with coordinated funding efforts and even a focus of a Manufacturing USA Institute. The potential benefit of these programs can be described as modest from a societal point of view, for example reducing vehicle mass by up to 25% with modest cost implications (under $5 per pound saved) and the ability to implement with existing manufacturing methods. Much more aggressive reductions in greenhouse gas production are necessary and possible, while delivering the same service. This is demonstrated with a higher-level design thinking exercise on an environmentally responsible lightweight vehicle, leading to the following criteria: lightweight, low aerodynamic drag, long-lived (over 30 years and 2 million miles), adaptable, electric, and used in a shared manner on average over 8 h per day. With these specifications, passenger-mile demand may be met with around 1/10 of the current fleet. Such vehicles would likely have significantly different designs and construction than incumbent automobiles. It is likely future automotive production will be more analogous to current aircraft production with higher costs per pound and lower volumes, but with dramatically reduced financial and environmental cost per passenger mile, with less material per vehicle, and far less material required in the national or worldwide fleets. Subsidiary benefits of this vision include far fewer parking lots, greater accessibility to personal transportation, and improved pedestrian safety, while maintaining a vibrant and engaging economy. The systemic changes to the business models and research and development directions (including lightweight design and manufacturing) are discussed, which could bring forth far more sustainable personal transportation.

Transients in creep are of fundamental importance. They are commonly described either by a change in the isotropic strength of a material due to an increase in dislocation density or by a change in directional hardening, often described by a backstress. Here we look at transients as developed by load redistribution in Finite Element simulations. Two types of material models are used. The first contains grains with binary strength; the other uses grains with a continuous distribution of strengths. It was found that the load redistribution process is an important source in transient yielding and creep. An equivalent stress quantity to track the strength of a sample during deformation is proposed. Using this quantity a single load shedding curve can be obtained for both the tensile and creep tests. This unifies the material constitutive behavior for the very different boundary conditions seen in creep and constant-rate testing.

Abstract

Vaporizing foil actuator welding is a form of impact welding, which can be carried out without the use of chemical explosives. Operating at smaller length scales, but with similar driving pressures as explosive welding, vaporizing foil actuator welding is capable of welding a wide variety of advanced and dissimilar metal combinations. With negligible heating developing during the process, thermal distortion does not occur, and the base-metal properties are retained in the weld. In this article, vaporizing foil actuator welding of an automotive grade aluminum and steel pair is discussed. A currently functional and complete welding system that can be used for research as well as low volume production is also discussed.

Laser impact welding (LIW) is a solid-state, collision-based welding process. Applications may include joining of dissimilar metals for small-scale parts such as those used in medical devices and microelectronics. The current work focuses on the development of the LIW process for industrial applications with commercial available materials. In this technique, a pulse of high power laser light was converted to kinetic energy through the ablation of a coating on the flyer surface. A transparent confining window directed the force of the expanding gas to launch a flyer toward a target plate. A suitable laser system with diagnostics is described. An experimental study of parameters affecting ablation pressure was conducted via an analysis of flyer deformation and launch velocity. A laminated multi-launch package with a CNC-based motion control welding apparatus was constructed with informed selection of components to optimize conversion efficiency. This joining system is used to demonstrate the LIW joining of aluminum and titanium.

Hemming is the last or one of the latest stage operations for the stamped parts. For this reason it has a critical importance on the performance and perceived quality of assembled vehicles. It is used to attach two sheet metal parts together or to improve appearance creating a smooth edge rather than a razor edge with burrs. However, designing the hemmed union is not always easy and is deeply influenced by the mechanical properties of the material of the bended part. Main problems for the automotive industry arise when bending aluminum alloys. Aluminum sheet is more difficult to hem due to its susceptibility to strain localization during the hemming process. This phenomenon produces cracking on the hemmed edge [1]. In order to avoid this problem and due to the limitations of conventional flanging and hemming technologies, the flange radii must be increased and a rope hem used (instead of the flat hem used with steels) when working with aluminum alloys. These changes on the design of the hem union give as a result a lower quality final product [2]. Dies and tools used for the hemming process are designed based on experience and on lengthy and costly die tryouts. Continuing with the development of new applications for the Electromagnetic Forming (EMF) technology, LABEIN-Tecnalia and Professor Glenn Daehn’s group from The Ohio State University carried out some first straight flat hemming experiments using the AA 6016 T4 aluminum alloy. The results obtained from these first trials are presented in this paper giving a first sight of the possibilities, advantages and disadvantages of using the Electromagnetic Forming technology for the hemming of aluminum sheet panels. Using a non-clouped FEM simulation method, the experimental results are compared to the ones obtained with the simulations. The future working line in developing this new application for the Electromagnetic Forming technology will be based on the results obtained by this study.

Intergranular corrosion is a significant concern for Al-Mg alloys when subjected to a corrosive salt-water environment. To address this issue, the standard composition of a 5XXX series aluminum alloy (AA5083) was modified in an attempt to improve the alloy’s overall corrosion resistance through alloying and thermal processing. The concept being that through alloying and heat treatments, desirable precipitate phases such as τ- and/or τ-copper rich phase(s) that are known to offer corrosion resistance would potentially form that could effectively improve intergranular corrosion behavior. Therefore, the chemical composition of standard AA5083 was modified by adding various amounts of copper and zinc. Sensitization heat treatments were then performed to determine the specific conditions under which these phases would form. LOM, SEM, STEM imaging and conventional TEM were used to analyze microstructural features. Corrosion was attributed to a network of detrimental Mg-rich grain boundary precipitates in the standard alloy. Alloying with Cu and Zn can offer improved intergranular corrosion behavior. The mechanism seems to be either by delaying or eliminating precipitation at the grain boundaries.

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The cold compaction of ceramic-metal powder blends by the cyclic application of pressure improves compacted density. This enhanced densification has been attributed to a repeated generation of mismatch strain between the matrix and reinforcement phases, in a process similar to that seen in the thermal cycling of fully dense composites. It was postulated that cyclic compression may also reduce density gradients and improve overall uniformity. To test this hypothesis, aluminum and alumina powders were mixed and consolidated under both monotonic and cyclic loading at room temperature. Three aspect ratios were used and double-action compaction was included. X-ray computed tomography (CT) shows that the spatial density of uniformity improved during cyclic compaction. The distribution of ceramic particles was found to be more uniform following pressure cycling, especially for compacts having lower aspect ratios. A composite with 40 pct reinforcement achieved nearly uniform full density following double-action cyclic compaction. Cyclic compaction improves overall density as well as density uniformity and reinforcement distribution uniformity.

The effect of cyclic pressure on the room temperature composite powder consolidation has been studied. Mixed metal and ceramic powders were consolidated under static and cyclic pressure at room temperature in constrained “uniaxial” consolidation. In this paper, five composite powder systems, Pb/TiO2, Pb/Sic, Al/Al2O3, Al/Sic and Zn/Al2O3, have been studied at 40% ceramic by volume. This complements an extensive study of Pb/Al2O2in static and cyclic consolidation that was reported earlier [1]. The experiments show that pressure cycling greatly enhances densification relative to static compaction at the same maximum pressures. The proposed reason for improved densification in cyclic pressure is that the pressure changes (ΔP) may directly induce plastic deformation due to elastic mismatch strains that develop between the metal and ceramic phases. These are induced owing to the compressibility difference (Δβ) between the two phases. The six powder systems studied to date (at many pressure cycle amplitudes) show that all the data for density change nearly collapse to one trend line when plotted against the dimensionless strain ratio, ΔβΔP/εo, where the numerator represents the linear elastic mismatch strain and εois the matrix yield strain. This term must exceed a value near 3 in order to significantly improve consolidation by pressure cycling. This effect is expected to have practical importance as the pressures required to improve consolidation are often accessible and the strengths of the compacts formed by pressure cycling are significantly greater than those produced in static consolidation.

One-dimensional numerical simulations of dynamic tensile tests have been carried out over a wide range of test velocities for materials having aHollomon-typeconstitutive law with power-law strain-rate sensitivity. A variety of values of the strain-hardening exponent and strain-rate-sensitivity index have been used to analyze the effect of inertia on tensile ductility. Results show that the total elongation of the specimen is enhanced by inertia at high test velocities. This inertial effect varies with the strain-hardening exponent and strain-rate-sensitivity index and can be scaled with the normalized material density and the test velocity. Based on these results, the critical test velocity for the onset of the inertial effect as a function of material parameters has been numerically determined. To account for the effect of inertia on the enhancement of tensile ductility, a simple phenomenological explanation has been proposed.

Thin rings have been rapidly expanded using large, transient magnetic fields to study the effect of deformation velocity on strains to failure of ductile metals. A classical electrodynamics analysis similar to one developed previously by Gourdin was employed to estimate sample velocities. Within expansion velocities studied (50 to 300 m/s), the experimental results show that ductility of Al 6061 and OFHC Cu increases monotonically with increasing velocity. In each case, sample strain at failure is almost twice as great at 300 m/s as in the static condition. Comparison to a one-dimensional rigid-viscoplastic dynamic finite element method analysis suggests that inertial effects are mainly responsible for enhanced ductility over a wide range of velocity.

The difference in creep strength between a base metal and a weld metal always produces a multiaxial stress state even if the macroscopic loading is uniaxial. In this study, weldments were formed between wrought 316 stainless steel and two types of 316 weld metals with slightly different creep properties and chemical compositions. Full-size 316 weldments, including base metal, heat-affected zone (HAZ) and welds, were creep tested at 650 °C. The multiaxial stress distributions in full-size 316 weldments were simulated by the finite element method (FEM). Three stress parameters, namely, the maximum principal stress (MPS), the yon Mises effective stress (VMS), and the principal facet stress (PFS), were used to correlate the local multiaxial stresses with local creep damage distributions and failure lifetime. Metallographic examination and creep rupture data showed that the PFS parameter gave the best prediction of the creep damage distribution caused by the multiaxial stresses in 316 weldments. This approach may have application in the design, life prediction, and in-service evaluation of weldments.

Spheroidized 1020, 1045, and 1090 steel samples were cold-rolled to large plastic strains. This lead to cracking by alligatoring in 1090 steel. At strains smaller than required for alligatoring, voids were observed to be widely distributed in all three steels. The nucleation, growth, and coalescence of voids were characterized with quantitative metallography and density measurements. The process leading to alligatoring was analyzed as three sub-processes: the evolution of voids, the formation of an initial crack, and the damaged material finally fracturing. The influence of rolling parameters on void growth under this nominally compressive stress state was also discussed.

•Direct solid-state joining of Ni-based superalloys (718, 625, 230) and Ti 6242.•Welded 6 dissimilar and 4 similar pairs via Vaporizing Foil Actuator (VFA) method.•Dissimilar Ni-Ni and Ni-Ti joints were stronger than similar joints in many cases.•Benchmarked dissimilar joint strength using lap shear and peel mechanical tests.•Characterized weld and peel surfaces with electron microscopy and spectroscopy.

The article presents information related to two solid-state collision welding processes including magnetic pulse welding (MPW) and laser impact welding (LIW). The MPW application's flexibility in many configurations are explained. Description of four configurations for plate-to-plate welding is provided.

The article focuses on a research on the low-energy impact spot welding of high-strength aluminum alloys A5052 and A7075. Topics discussed include reducing the strength of the heat-affected zone (HAZ) and vaporizing foil actuator welding (VFAW); joint efficiency, improvement, and generated pressures in VFAW, and creating a lap-joint specimens and subjecting it to lap shear testing, microhardness testing, and imaging.